Different toxic oxygen metabolite species may be generated in the lung by different mechanisms (from bleomycin, iron and oxygen reactions, lung cell oxidative metabolism, alveolar macrophages (AM) and/or recruited neutrophils) at different sites, different times and with different consequences during the development of bleomycin-induced interstitial lung disease (ILD). However, the important, fundamental concept that oxygen metabolites contribute to bleomycin-induced ILD is suspect because the effect of addition of oxygen metabolite scavengers on bleomycin-induced lung injury has not been determined and because no good methods exist for assessing oxygen metabolites in biological systems. Our hypothesis is (1) that addition of oxygen metabolite scavengers, (such as the highly permeable, non-toxic dimethylthiourea (DMTU) or long-lived, polyethylene-glycol conjugated superoxide dismutase or catalase (PEG-SOD + PEG- CAT)) will decrease lung inflammation and injury which occurs following bleomycin and (2) that bleomycin-induced increases in oxygen metabolite production will be reflected by increases in DMTU consumption, DMTU project formation and/or lung tissue oxidized glutathione (GSSG) which (along with lung injury) are preventable by simultaneous addition of oxygen metabolite scavengers. Our studies support this premise: DMTU decreased bleomycin-induced injury to AM in vitro. DMTU was also consumed in cultured lung endothelial cells and isolated lungs according to added amounts of hydrogen peroxide and corresponding injuries. DMTU consumption specificity was suggested when added oxygen metabolite scavengers (catalase or erythrocytes) decreased DMTU consumption (and injury) and DMTU consumption did not occur with added leukotrienes, elastase, trypsin, PAF or oleic acid. Addition of PEG-SOD + PEG-CAT also decreased lung tissue GSSG increases and injury in rats given hyperoxia. Finally, DMTU consumption and DMTU product formation from reaction of DMTU with hydrogen peroxide can be very sensitively measured by HPLC. Our immediate objectives now are to determine 1) if treatment with oxygen metabolite scavengers will decrease lung injury in rabbits given bleomycin intratracheally and 2) if scavenging of oxygen metabolites is indeed the mechanism by which scavengers decrease bleomcyin-induced lung injury by assessing DMTU consumption, DMTU product formation and lung tissue oxidized glutathione (GSSG). This work will provide new information and approaches for assessment of oxygen metabolites which will provide our understanding of basic mechanisms responsible for ILD and other disorders.